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Volumetric Properties of High RAP Mixtures through Bulk Specific Gravities Analysis

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This study investigates the volumetric properties of High Reclaimed Asphalt Pavement (RAP) mixtures by analyzing the calculated bulk specific gravities of RAP and constituent aggregates. With around 100 million tons of RAP produced annually, understanding its properties is essential for effective utilization in hot mix asphalt (HMA). The research compares multiple methods for obtaining bulk specific gravity (Gsb) and assesses their influence on volumetric mix design parameters such as Voids in Mineral Aggregate (VMA). Results indicate optimal methods for incorporating RAP in Superpave mixtures.

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Volumetric Properties of High RAP Mixtures through Bulk Specific Gravities Analysis

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  1. Volumetric Properties of High RAP Mixtures Based on Calculated Bulk Specific Gravities of RAP and Constituent Aggregates NassimSabahferMustaqueHossain, Ph.D.,P.E. Department of Civil EngineeringKansas State University

  2. Outline • Background • Problem Statement • Objective • Methodology • Laboratory Testing • Results • Conclusions & Recommendations • Acknowledgements

  3. Background - Reclaimed Asphalt Pavement (RAP) • Approx. 100 million tons of RAP produced each year and 80 million tons are reused • Useful alternative to virgin aggregates in HMA: • Reduces cost • 20% RAP with 5% binder • 1% savings in new binder • Enables recycling • Conserves energy RAP Stockpile at Shilling Construction Co., Manhattan, KS

  4. RAP Usage in the US

  5. Problem Statement • Superpave mix design is predominantly used now and permits use of RAP • Superpave volumetric mix design is highly dependent on properties like VMA, VFA, and Dust-to-Binder Ratio • These parameters need blend bulk aggregate specific gravity in the calculation process • RAP aggregate specific gravity is tricky

  6. Objectives • Compare RAP aggregate bulk specific gravity (Gsb) obtained from various methods • Investigate influence of this Gsb on the calculated VMA • Investigate effect of asphalt absorption assumption • Study RAP maximum theoretical specific gravity (Gmm) as RAP Gsb

  7. Methodology • Choose RAP sources (5) • Run maximum specific gravity tests (Gmm) on two replicates of each RAP • Obtain RAP aggregates via (a) extraction and (b) ignition oven burn off • Sieve into coarse (plus #4) and fine (minus #4) fractions • Run bulk specific gravity tests and compare • Compute VMA and compare

  8. RAP Gradations (12.5 mm NMAS)

  9. Measured RAP Properties * Ignition oven

  10. Gmm Test (KT-39)

  11. Coarse and Fine Aggregates in RAP Materials

  12. RAP Aggregate Bulk Specific Gravity • Method #1 • Split extracted aggregates into coarse and fine fractions • Determine bulk specific gravity of each fraction • Method #2 • Same as #1; use burned off aggregates

  13. RAP Aggregate Bulk Specific Gravity • Method #3 • Determine RAP Gmm • Determine RAP binder content • Calculate Gse of RAP: • Assume or know asphalt absorption, Pba • Calculate Gsb of RAP aggregate:

  14. Aggregate Specific Gravity Test Results

  15. Statistical Analysis • Comparison of Gsb

  16. Changes in Gsb as a function of asphalt absorption

  17. VMA Obtained Using Gsb from Different Methods (Konza RAP)

  18. VMA Obtained Using Gsb from Different Methods (Shilling RAP)

  19. Statistical Analysis

  20. Differences in calculated VMA as a function of RAP content

  21. Conclusions • Gsbsobtained from the ignition oven and solvent extraction methods are similar but both are different from that based on Gse • Statistically RAP Gmm is not significantly different from Gsbobtained from the ignition oven or solvent extraction method • VMA obtained from Gse-based Gsb is significantly different from the VMA’s obtained from other Gsbs • Difference in VMA increases considerably as the RAP content increases

  22. Recommendations • RAP aggregate Gsb using either from the extraction or the ignition oven test method should be used in design of Superpave mixtures with RAP

  23. Acknowledgements • This study has been sponsored by the Kansas Department of Transportation (KDOT) • Project Monitor: Brian Coree, Ph.D., P.E.

  24. Thank You

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